Dr. Fan Zhang, associate professor of physics in the School of Natural Sciences and Mathematics, is an author of a study published on Oct. 6 in the journal Nature that demonstrates the exotic behavior in bilayer graphene, which is a naturally occurring, two-atom thin layer of carbon atoms arranged in two honeycomb lattices stacked together.

The quantum Hall effect is a macroscopic phenomenon in which the transverse resistance in a material changes by quantized values in a stepwise fashion. It occurs in two-dimensional electron systems at low temperatures and under strong magnetic fields. In the absence of an external magnetic field, however, a 2D system may spontaneously generate its own magnetic field, for example, through an orbital ferromagnetism that is produced by interactions among electrons. This behavior is called the quantum anomalous Hall effect.

“When the rare quantum anomalous Hall effect was investigated previously, the materials studied were complex,” Zhang said. “By contrast, our material is comparably simple, since it just consists of two layers of graphene and occurs naturally.”

Dr. Thomas Weitz, an author of the study and a professor at the University of Göttingen, said: “Additionally, we found quite counterintuitively that even though carbon is not supposed to be magnetic or ferroelectric, we observed experimental signatures consistent with both.”

In research published in 2011, Zhang, a theoretical physicist, predicted that bilayer graphene would have five competing ground states, the most stable states of the material that occur at a temperature near absolute zero (minus 273.15 degrees Celsius or minus 459.67 degrees Fahrenheit). Such states are driven by the mutual interaction of electrons whose behavior is governed by quantum mechanics and quantum statistics.

“We predicted that there would be five families of states in bilayer graphene that compete with each other to be the ground state. Four have been observed in the past. This is the last one and the most challenging to observe,” Zhang said.

In experiments described in the Nature article, the researchers found eight different ground states in this fifth family that exhibit the quantum anomalous Hall effect, ferromagnetism and ferroelectricity simultaneously.

“We also showed that we could choose among this octet of ground states by applying small external electric and magnetic fields as well as controlling the sign of charge carriers,” Weitz said.

The ability to control the electronic properties of bilayer graphene to such a high degree might make it a potential candidate for future low-dissipation quantum information applications, although Zhang and Weitz said they are primarily interested in revealing the “beauty of fundamental physics.”

“We predicted, observed, elucidated and controlled a quantum anomalous Hall octet, where three striking quantum phenomena — ferromagnetism, ferroelectricity and zero-field quantum Hall effect — can coexist and even cooperate in bilayer graphene,” Zhang said. “Now we know we can unify ferromagnetism, ferroelectricity and the quantum anomalous Hall effect in this simple material, which is amazing and unprecedented.”

Other authors of the Nature article include UT Dallas physics doctoral student Tianyi Xu and researchers from the University of Göttingen and the Ludwig Maximilian University of Munich.

Zhang’s research is funded by the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory and the National Science Foundation.

Story Source:

Materials provided by University of Texas at Dallas. Original written by Amanda Siegfried. Note: Content may be edited for style and length.

New regulation as initial spark

Recently, because the first global regulation for Automated Lane Keeping Systems (ALKS) has been in force since the beginning of 2021. This law resolves the road approval dilemma, as Eichberger explains: “Until now, regulatory authorities did not know how to test and approve autonomous driving systems. The vehicle manufacturers, in turn, did not know what requirements the systems had to meet in order to be approved.” In the regulations, the approval criteria for highly automated systems (autonomous driving level 3) up to a maximum speed of 60 km/h have now been specified for the first time on the basis of a traffic jam assistant. When the assistant is activated, responsibility for control is transferred to the machine. The driver may take their hands off the steering wheel, but has to immediately take over again in the event of a malfunction. The system must recognize that the person behind the wheel is capable of doing this.

Based on this regulation, Eichberger and his research partners from Fraunhofer Austria, AVL and JOANNEUM RESEARCH have developed an efficient method over the last few months by which the readiness to take over control can be tested safely, efficiently, and to a high degree realistically in a driving simulator and the results can be used for the certification of ALKS systems.

Identical machine perception of the environment

Processes were required to prove the validity of the driving simulation using the test drive. The basis for this was a direct comparison — driving simulation and real driving (the AVL test track in Gratkorn, Styria, served as the test location) had to match as closely as possible. Here, the machine perception of the environment posed a challenge. Figuratively speaking, machine perception is the sensory organs of the vehicle. It has the task of precisely recording the vehicle’s surroundings — from the landscape and environmental objects to other road users — so that the driving assistance system can react appropriately to the situation. Eichberger: “If this is to run the same as in reality, the environments in the simulation have to match the real environment to the exact centimetre.”

Transferring the driving routes to the driving simulator

his accuracy is achieved using so-called “Ultra High Definition Maps” (UHDmaps®) from JOANNEUM RESEARCH (JR), one of the world’s leading research institutions in the field of digital twins. “We use a mobile mapping system to measure the test environments. Finally, a seamless 3D map with an extremely high level of detail is created from the measurement data. In addition to traffic infrastructure objects such as traffic signs, lane markings and guard rails, vegetation and buildings are also represented in this map,” says Patrick Luley, head of the research laboratory for highly automated driving at the DIGITAL Institute. While comparable accuracy can be achieved with manual 3D modelling, JR’s automated UHD mapping process is many times cheaper and faster.

The high-resolution 3D environment is finally transferred to the driving simulator. This is where the Fraunhofer Austria team come in. Volker Settgast from the Visual Computing business unit: “We prepare the data in such a way that the 3D environment can be displayed at high speed.” Even reflective and transparent surfaces or trees and bushes blown by the wind can be perceived naturally. Depending on the test scenario, additional vehicles or even people can then be added to the virtual environment.

The validation is finally verified with the help of comparative runs on the real route. “With our method, it is possible for car manufacturers to easily compare and validate a certain sampling on the real track and in the driving simulator. This means that the test can ultimately be transferred from the real track to the driving simulator,” says Eichberger. The TU Graz researcher and his team are now working on setting up virtual approval tests over the next few months.

Story Source:

Materials provided by Graz University of Technology. Original written by Christoph Pelzl. Note: Content may be edited for style and length.

Since the first observation of merging black holes by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015, astronomers have been repeatedly surprised by their large masses. Though they emit no light, black hole mergers are observed through their emission of gravitational waves — ripples in the fabric of spacetime that were predicted by Einstein’s theory of general relativity. Physicists originally expected that black holes would have masses less than about 40 times that of the Sun, because merging black holes arise from massive stars, which can’t hold themselves together if they get too big.

The LIGO and Virgo observatories, however, have found many black holes with masses greater than that of 50 suns, with some as massive as 100 suns. Numerous formation scenarios have been proposed to produce such large black holes, but no single scenario has been able to explain the diversity of black hole mergers observed so far, and there is no agreement on which combination of formation scenarios is physically viable. This new study, published in the Astrophysical Journal Letters, is the first to show that both large and small black hole masses can result from a single pathway, wherein the black holes gain mass from the expansion of the universe itself.

Astronomers typically model black holes inside a universe that cannot expand. “It’s an assumption that simplifies Einstein’s equations because a universe that doesn’t grow has much less to keep track of,” said Kevin Croker, a professor at the UH M?noa Department of Physics and Astronomy. “There is a trade-off though: predictions may only be reasonable for a limited amount of time.”

Because the individual events detectable by LIGO — Virgo only last a few seconds, when analyzing any single event, this simplification is sensible. But these same mergers are potentially billions of years in the making. During the time between the formation of a pair of black holes and their eventual merger, the universe grows profoundly. If the more subtle aspects of Einstein’s theory are carefully considered, then a startling possibility emerges: the masses of black holes could grow in lockstep with the universe, a phenomenon that Croker and his team call cosmological coupling.

The most well-known example of cosmologically-coupled material is light itself, which loses energy as the universe grows. “We thought to consider the opposite effect,” said research co-author and UH M?noa Physics and Astronomy Professor Duncan Farrah. “What would LIGO — Virgo observe if black holes were cosmologically coupled and gained energy without needing to consume other stars or gas?”

To investigate this hypothesis, the researchers simulated the birth, life, and death of millions of pairs of large stars. Any pairs where both stars died to form black holes were then linked to the size of the universe, starting at the time of their death. As the universe continued to grow, the masses of these black holes grew as they spiraled toward each other. The result was not only more massive black holes when they merged, but also many more mergers. When the researchers compared the LIGO — Virgo data to their predictions, they agreed reasonably well. “I have to say I didn’t know what to think at first,” said research co-author and University of Michigan Professor Gregory Tarlé. “It was a such a simple idea, I was surprised it worked so well.”

According to the researchers, this new model is important because it doesn’t require any changes to our current understanding of stellar formation, evolution, or death. The agreement between the new model and our current data comes from simply acknowledging that realistic black holes don’t exist in a static universe. The researchers were careful to stress, however, that the mystery of LIGO — Virgo’s massive black holes is far from solved.

“Many aspects of merging black holes are not known in detail, such as the dominant formation environments and the intricate physical processes that persist throughout their lives,” said research co-author and NASA Hubble Fellow Dr. Michael Zevin. “While we used a simulated stellar population that reflects the data we currently have, there’s a lot of wiggle room. We can see that cosmological coupling is a useful idea, but we can’t yet measure the strength of this coupling.”

Research co-author and UH M?noa Physics and Astronomy Professor Kurtis Nishimura expressed his optimism for future tests of this novel idea, “As gravitational-wave observatories continue to improve sensitivities over the next decade, the increased quantity and quality of data will enable new analysis techniques. This will be measured soon enough.”

The study found that sugary drink taxes only reduce purchasing if price tags at stores mention that consumers are paying that tax when they buy the drink.

“If cities want these policies to be effective, they need to regulate how these sugary drinks are labeled at the stores where they are sold — and they currently don’t do that,” said Grant Donnelly, lead author of the study and assistant professor of marketing at The Ohio State University’s Fisher College of Business.

The findings suggest that price tags should mention the tax, but not the amount, because consumers tend to overestimate how much the tax is, Donnelly said. If they know the true size of the tax, they are more willing to pay it.

Among the cities that currently have a tax on sugary drinks are Philadelphia, San Francisco, Seattle, and Boulder.

The study was published online recently in the journal Psychological Science.

The research included a field study at two convenience stores in San Francisco, which currently has a tax on sugary drinks of 1 cent per ounce — an added 12 cents to a 12-ounce drink.

Researchers varied the price tags placed on the sugary drinks over the eight-week study. There were three price tags that were rotated: One that simply said the price for the 12-ounce drink ($1.52); one that had the price and the message “Includes SF Sugary Drink Tax”; and one that included the same message and added that the proceeds of the tax would support local university student programs.

All non-sugary drinks, which were not subject to the tax, simply had the price of the drink, which was $1.40.

The researchers compared sales of the drinks during the study period to the two immediately preceding weeks. During this time, the sugary drink tax was in effect, but there were no price tags on any drinks. They also compared sales to the two years preceding the tax.

Results showed that sales of sugary drinks were not lower during the two weeks before the study began, compared to sales in the two years before the tax. In other words, the tax itself did not reduce purchases of sugary drinks.

The researchers then looked at the effects of the three different price tags during the course of the study.

Results showed that the share of sugary drinks bought when the tags simply showed the price (47%) was not significantly different from the two-week period before the study.

But the share of sugary drinks purchased did decline slightly (45%) when the tags mentioned the price included the added tax.

Results showed that most consumers who chose to avoid sugary drinks with the added tax chose a drink that was not subject to the tax.

“Consumers are averse to taxes, so when they learn that their favorite drink has this sugary beverage tax, some are less interested in buying it,” Donnelly said.

“They generally substitute for healthier beverages, like bottled water. So the taxes do not seem to hurt the stores that sell drinks.”

Tags that noted where the taxes would be spent had no significant effect beyond the tags that simply noted the added tax.

In a separate online study, the researchers asked participants who drank sugary beverages to estimate what the tax would be on a 12-ounce can of their favorite beverage that cost $1.52. The average estimate was 40 cents — much higher than the 12 cents actually levied in San Francisco.

Another study found that when consumers were told the tax was only 12 cents, they reported they were much more likely to still purchase the drink.

“People don’t like taxes, but they think this tax is much higher than it actually is,” Donnelly said. “If you tell consumers the true cost of the tax, it is no longer effective in reducing purchases.”

The bottom line, he said, is that if cities want these policies to be effective at reducing consumption of unhealthy beverages, they must mandate that tags mention the added tax — but not reveal how much it is.

Co-authors on the study were Paige Guge and Ryan Howell of San Francisco State University and Leslie John of Harvard University.

Co-author Richard Ostfeld, a disease ecologist at Cary Institute of Ecosystem Studies, comments, “Results of our long-term study on wild white-footed mice do not support the long-held assumption, sometimes applied to vertebrates more broadly, that physical impairments reduce measures of fitness such as survival, movement, and mass.”

The research team analyzed 26 years of data from a long-term mark-recapture program that Ostfeld initiated on Cary Institute’s Millbrook, NY property in 1991. Small mammals were trapped at six plots in deciduous forest dominated by oaks and maples. Catch-and-release trapping occurred every 3-4 weeks over 2-3 consecutive days between May and November using live traps baited with oats.

Mice were given metal ear-tags upon first capture, and data on sex, age, mass, ectoparasite load (e.g., bot fly larvae, ticks), and location were recorded. In addition, trappers took detailed notes about the physical features of each animal.

Lead author Francesca Rubino of the UC Davis School of Veterinary Medicine was a former Project Assistant in the Ostfeld Lab. She explains, “White-footed mice are survivors. We know they thrive in degraded forests and can tolerate high parasite loads. We were interested in determining if this tolerance extended to physical impairments.”

To assess the impact of physical impairments on the fitness of mice, trapping notes from 1991 to 2016 were reviewed. Mice with the following impairments were included in the study: missing, partially missing, or broken tails; missing, partially missing, or broken/deformed limbs; and missing eyes or cataracts. Survival was estimated by persistence time on the trapping plots. Body mass, movement, and ectoparasite burden (larval bot fly and ticks) were also analyzed.

“To our knowledge, no prior study has included as big a sample size of individuals or as long a time series. Having mark-recapture records on a large number of mice both before and after their impairment provided us with a unique opportunity to distinguish cause-effect relationships from mere correlation.” Ostfeld explains.

Of the 27,244 mice, 2% (543) had visible physical impairments. Although tail and limb impairments were associated with more black-legged ticks and mice with cataracts had more bot fly larvae, mice with impairments were just as likely as their unmpaired counterparts to survive on the trapping plots. Mice with eye and tail impairments had greater mass than unimpaired mice, and mice with tail impairments had larger home ranges.

Rubino explains, “We found no evidence that physical impairments in white-footed mice were associated with decreased fitness. On the contrary, looking across standard measures of fitness, mice with impairments performed at least as well, on average, as mice without impairments.”

With Ostfeld adding, “Mice appear able to compensate for broken or missing major appendages and for partial or total loss of vision in ways that generally avoid compromising longevity, body condition, movement, or protection from ectoparasites.”

The authors note that this resilience is consistent with prior studies revealing the ability of mice to tolerate infection by some parasites. Whether this tolerance to injury and infection is shared with other species, and if so, what mechanisms might underlie high tolerance, are unknown, but worthy of further study.

“This study is both powerful — more than 27,000 wild mice over 26 years — and surprising,” says Doug Levey, a program director in NSF’s Division of Environmental Biology, which provided grant support for the work. “Until now, few ecologists would have said that impaired mice live as long as mice that are free of impairments.”

“Our findings challenge broader assumptions that physical impairments reduce the fitness of their bearers and are inconsistent with the devaluation of impaired individuals that pervaded early thinking in evolutionary biology,” Ostfeld concludes.

This research was supported in part by the US National Science Foundation’s Long Term Research in Environmental Biology (LTREB) program (grant numbers: DEB 0075277, DEB 0444585, DEB 0949702, and DEB 1456527).